TW201410755A - Polyester film for cold forming and manufacturing method thereof - Google Patents

Abstract

The present invention provides a polyester film for cold forming, which contains poly butylene terephthalate (PBT) and poly ethylene terephthalate (PET), wherein the mass ratio of PBT and PET (PBT/PET) is 30/70 to 80/20.

Description

Polyester film for cold rolling forming and method for producing same

The present invention relates to a cold-rolling polyester film which can be cold-rolled, such as stretch forming or deep drawing, and a method for producing the same.

In the past, a metal can was used as a lithium ion secondary battery. However, in order to reduce the weight and shape of the lithium ion secondary battery, the exterior is replaced by a laminate of a metal foil laminated plastic film such as aluminum foil. The body of the bag. Such a bag body is indispensable for moisture resistance, sealing property, puncture resistance, insulation property, heat resistance/cold resistance, formability, and the like, and thus the laminate body is made of polyester film/polyfluorene from the outside to the inside. The composition of the amine film/metal foil/seal film.

In a miniaturized and thinned electronic device, in order to efficiently provide a printed circuit board, other members, and a lithium ion secondary battery, it is necessary to form a corner portion of the battery exterior into a sharp shape. Then, in the cold-rolling forming such as the stretch forming or the deep-drawing, the development of the polyamide film having excellent moldability is emphasized, and in Patent Documents 1 and 2, a polyamide film having a small mechanical property is proposed. The impact strength is above 30000 J/m, and the tensile strength in the four directions (0°, 45°, 90°, 135°) to the fracture is 150 N/mm ² or more, and the elongation in the four directions is 80%. the above.

Advanced technical literature

Patent Document 1: Japanese Laid-Open Patent Publication No. 2000-123800

Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-022336

However, the physical properties of such a polyamide membrane are achieved by substantially extending the polyamide resin in an inflation process. Therefore, the polyamide film which is stretched by the mass production-oriented tenter method cannot be used for this purpose, and the technique of cold-rolling the laminated body of the laminated polyimide film cannot be widely used.

Further, the polyamide film tends to be degraded by the decomposition reaction of the guanamine group in the presence of an acid or an electrolyte. Therefore, when the surface layer of the lithium ion secondary battery is a polyimide film, if the electrolyte or the acidic substance is spilled during the liquid injection step and adheres to the polyimide film, the film may be broken, so the lithium ion secondary battery is externally mounted. The outermost layer needs to be laminated with a polyester film excellent in acid resistance and electrolyte resistance.

An object of the present invention is to provide a polyester film which is excellent in moldability in cold-rolling forming such as stretch forming or deep-drawing, and which can be formed into a sharp shape. Next, a laminate composed of a polyester film/metal foil/sealing film can be used for a lithium ion secondary battery by using the film.

In order to solve the above problems, the inventors of the present invention carefully examined and found that a polyester film containing polybutylene terephthalate and polyethylene terephthalate in a specific ratio was cooled in a stretch forming or a deep drawing forming. The roll formability is excellent in formability and can be formed into a sharp shape, thereby completing the present invention.

That is, the focus of the present invention is as follows.

(1) A polyester film for cold roll forming, comprising a polyester film of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), characterized by PBT and PET The mass ratio (PBT/PET) is 30/70 to 80/20.

(2) The polyester film for cold-rolling forming according to (1), wherein the heat-shrinkage ratio in the longitudinal direction (MD) and the heat-shrinkage ratio in the width direction (TD) are 5 after heat treatment at 160 ° C for 15 minutes. Up to 20%.

(3) The polyester film for cold-rolling forming according to (1), wherein the polybutylene terephthalate (PBT) contains 0 to 15% of phthalic acid as an acid component.

(4) The polyester film for cold-rolling forming according to (1), wherein the transesterification index of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) is 1 to 10%.

(5) A method for producing a polyester film for cold-rolling forming, which is a method for producing a polyester film for cold-rolling forming according to any one of the above (1) to (4), wherein In the long direction (MD) and the width direction (TD), the surface magnification (MD stretching ratio × TD stretching ratio) is 6 to 20 times, and the stretching ratio (MD stretching ratio / TD stretching ratio) is 0.4 to 1.

(6) The method for producing a polyester film for cold-rolling forming according to the above aspect, wherein the MD stretching ratio is 2 to 4 times and the TD stretching ratio is 3 to 5 times.

(7) A laminated film in which a metal foil and a sealing film are sequentially laminated on the polyester film for cold-rolling forming according to any one of the above (1) to (4).

According to the present invention, it is possible to provide a polyester film which is excellent in moldability in cold-rolling forming such as stretch forming or deep-drawing, and which can be formed into a sharp shape. The polyester film of the present invention has good acid resistance to hydrofluoric acid and good resistance to electrolyte solution, so that a laminate film composed of a polyester film/metal foil/sealing film can be used for lithium ion two by using the film. The secondary battery is installed outside.

Fig. 1 is a partial enlarged view of a peak (Sab, Sba, Saa, Sbb) caused by transesterification in the NMR chart of the film of the present invention.

The invention is described in detail below.

The polyester film of the present invention contains polybutylene terephthalate (PBT) and polyethylene terephthalate (PET).

In the present invention, polybutylene terephthalate (PBT) is obtained by using terephthalic acid and 1,4-butanediol as a polymerization component, and may be copolymerized with other components.

The copolymerization component is not particularly limited, and examples of the acid component include isophthalic acid, phthalic acid, 2,6-naphthalene dicarboxylic acid, sodium isophthalate-5-sulfonate, oxalic acid, succinic acid, and adipic acid. , azelaic acid, sebacic acid, lauric acid, dimer acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, pyroic acid, mesaconic acid, cyclohexanedicarboxylic acid, etc. Carboxylic acid; 4-hydroxybenzoic acid, ε-caprolactone, lactic acid, and the like.

Further, examples of the alcohol component include ethylene glycol, diethylene glycol, 1,3-propanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, triethylene glycol, and polyethylene glycol. , an ethylene oxide addition product of polypropylene glycol, polytetramethylene ether glycol, bisphenol A and bisphenol S, and the like.

Further, a small amount of 1,2,4-benzenetricarboxylic acid, 1,3,5-benzenetricarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid, trimethylolpropane, glycerin, and neopentyl can be used. A trifunctional compound such as an alcohol or the like.

These copolymer components may be used in combination of two or more kinds.

In the present invention, when a copolymer is used as the polybutylene terephthalate (PBT), the kind and ratio of the copolymerization component can be appropriately selected, but it is preferably relative to the whole The alcohol component 1,4-butanediol is 80 mol% or more, more preferably 90 mol% or more. When the 1,4-butanediol is less than 80 mol%, the melting point is lower than the range described later, and as a result, the crystallinity is lowered to lower the heat resistance of the film.

In the polyester film of the present invention, the melting point derived from polybutylene terephthalate (PBT) is preferably from 200 to 223 ° C, more preferably from 210 to 223 ° C. When the melting point is less than 200 ° C, the crystallinity of polybutylene terephthalate (PBT) is low, and as a result, the heat resistance of the film is lowered.

The polyethylene terephthalate (PET) of the present invention is a copolymerization component of terephthalic acid and ethylene glycol, and may be copolymerized with other components.

The copolymerization component is not particularly limited, and examples thereof include those exemplified in the above polybutylene terephthalate (PBT).

The acid component to be copolymerized is preferably isophthalic acid from the viewpoint of easily adjusting the melting point described below. In the polyethylene terephthalate (PET), the content of isophthalic acid is preferably from 0 to 15 mol%, more preferably from 0 to 12 mol%, based on the total acid component.

In the polyester film of the present invention, the melting point derived from polyethylene terephthalate (PET) is preferably from 230 to 256 ° C, more preferably from 236 to 256 ° C. When the melting point is less than 230 ° C, the crystallinity of polyethylene terephthalate (PET) is low, and as a result, the heat resistance of the film is lowered.

In the polyester film of the present invention, the mass ratio of polybutylene terephthalate (PBT) to polyethylene terephthalate (PET) (PBT/PET) must be 30/70 to 80/20, and then In order to obtain sufficient formability in cold rolling forming, it is preferably 40/60 to 70/30.

When the ratio of polybutylene terephthalate (PBT) in the polyester film exceeds 80% by mass, the properties of polybutylene terephthalate (PBT) having high crystallinity are apparently exhibited. The laminated film obtained by laminating a metal film of a polyester film and a sealing film has a low formability and impact resistance, and the adhesiveness with a metal foil also falls. On the other hand, when the ratio of polybutylene terephthalate (PBT) is less than 30% by mass, the tensile stress is increased, and the formability of the laminated film is lowered.

In particular, when the ratio of polybutylene terephthalate (PBT) in the polyester film is 40 to 70% by mass, the obtained laminated film has good followability in forming in cold rolling, and does not cause voids due to film deformation ( Void) causes whitening, and does not cause micro-cracks, and is excellent in adhesion to metal foil, and can be deformed greatly without damaging the metal foil. As a result, the laminated film can be formed into a sharp shape, and a lithium ion secondary battery having a high degree of freedom in shape can be obtained.

The raw material polybutylene terephthalate (PBT) used for producing the polyester film of the present invention preferably has an ultimate viscosity of 0.75 to 1.6 dl/g, and further, a raw material polyethylene terephthalate (PET). Preferably, the ultimate viscosity is from 0.65 to 1.0 dl/g.

Further, the ultimate viscosity after the melt mixing is preferably from 0.75 to 1.2 dl/g. If the ultimate viscosity after melt mixing is less than 0.75 dl/g, the resulting laminated film may be broken during cold rolling and the productivity may be greatly lowered. On the other hand, if the ultimate viscosity after melt mixing exceeds 1.2 dl/g, the load of the melt extruder becomes large in the production step of the film, and the production speed has to be sacrificed, and further, the melting of the resin in the extruder is required. The residence time is too long, and the reaction between the polyester resins is excessively performed, which causes deterioration of the film properties, and as a result, the physical properties of the laminated film are lowered. In addition, the production of a material having a high ultimate viscosity is a cause of cost increase due to a relatively long polymerization time or a long polymerization step.

The polymerization method of the raw material polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) is not particularly limited, and for example, polymerization can be carried out by a transesterification method or a direct polymerization method. Examples of the transesterification catalyst include Mg, Mn, Zn, Ca, Li, and Ti. Oxide or acetate. Further, examples of the polycondensation catalyst include oxides of Sb, Ti, and Ge, and acetates.

Since the polyester after polymerization contains a monomer or an oligomer, acetaldehyde or tetrahydrofuran as a by-product, it is preferred to carry out solid phase polymerization at a temperature of 200 ° C or higher under a reduced pressure or an inert gas flow.

In the polymerization of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), additives such as an antioxidant, a thermal stabilizer, an ultraviolet absorber, an antistatic agent, and the like may be added as needed. The antioxidant is, for example, a hindered phenol-based compound or a hindered amine-based compound, and the thermal stabilizer is, for example, a phosphorus compound. Examples of the ultraviolet absorber include a diphenylketone-based compound and a benzotriazole-based compound. Further, as a reaction inhibitor between polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), it is preferred to add conventionally known before, during, and after polymerization. Phosphorus compound.

After the treatment of the polyester film of the present invention at 160 ° C for 15 minutes, the heat shrinkage ratio in the film length direction (MD) and the width direction (TD), that is, the MD heat shrinkage ratio and the TD heat shrinkage ratio are preferably 5 to 20%, more preferably 5 to 15%. When the heat shrinkage rate of the polyester film is less than 5%, the resulting laminated film may deteriorate in adhesion to the metal foil. On the other hand, when the heat shrinkage ratio exceeds 20%, shrinkage wrinkles may occur in the film when the laminate is laminated, or the obtained laminated film may be curled.

The heat shrinkage rate of the polyester film can be adjusted by changing the heat setting temperature at the time of the stretching step. By setting a high heat setting temperature, the degree of crystallization of the polyester film is increased, and the heat shrinkage rate can be lowered. Conversely, by setting a low heat setting temperature, the degree of crystallization of the polyester film is lowered, and the heat shrinkage rate can be improved.

The polyester film of the present invention is preferably polybutylene terephthalate (PBT). The transesterification index with polyethylene terephthalate (PET) is from 1 to 10%, more preferably from 3 to 7%. The laminated film of the polyester film having a transesterification index within the above range has good deformation followability in cold rolling forming, and does not adhere to the processing jig for cold rolling forming, and the resulting forming system is small in friction. The increase in surface uniformity also reduces the cracking of the metal foil during cold rolling.

The method of adjusting the transesterification index within the above range is not particularly limited, but it can be adjusted to adjust polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) in an extruder. The melting temperature, the degree of mixing in the extruder, and the residence time in the extruder are adjusted. The melt-mixing method is not particularly limited, and examples thereof include a method of melt-mixing the mixed raw material sheets in the same extruder, or a method of mixing and melting after mixing with different extruders, etc., but controlling the transesterification reaction. It is better to look at the latter method.

In addition, the transesterification index is greatly affected by the type, amount, and residual viability of the polymerization catalyst of the polyester. Therefore, techniques such as selecting a catalyst, optimizing the amount of the catalyst, and adding a catalyst activity inhibitor such as a phosphorus compound can be used in combination.

The method for producing the polyester film of the present invention includes the following methods.

That is, the mass ratio (PBT/PET) of polybutylene terephthalate (PBT) to polyethylene terephthalate (PET) is 30/70 to 80/20, and The inside of the extruder was melted and mixed at a temperature of 250 to 280 for 3 to 15 minutes, and then extruded in a sheet form through a T die. The sheet was adhered to a cooling cylinder whose temperature was adjusted to room temperature or lower, and cooled to obtain an unstretched film.

The obtained unstretched film was introduced into a simultaneous biaxial stretching machine, and biaxially stretched simultaneously in the longitudinal direction (MD) and the width direction (TD) at a temperature of 50 to 150 °C.

In the biaxial stretching, the area magnification (MD stretching ratio × TD stretching ratio) is preferably 6 Up to 20 times, more preferably 8.75 to 15.75 times. When the surface magnification is more than 20 times, the in-plane alignment of the film is promoted to increase the crystallization, and the obtained laminated film cannot be formed into a form during cold-rolling, and cracks or delamination may occur. On the other hand, if the surface magnification is less than 6 times, the film strength is insufficient, and thus the resulting laminated film is cracked during cold rolling.

Further, the stretching ratio ratio (MD stretching ratio / TG stretching ratio) is preferably from 0.4 to 1, more preferably from 0.55 to 1. When the ratio of the stretching ratio is outside this range, the MD and TD in the plane generate an alignment strength and the alignment balance is deteriorated, so that the obtained laminated film may be easily cracked or wrinkled in the direction of weak alignment during cold rolling. The problem.

In order to obtain the above-described surface magnification and stretching ratio, as the stretching ratio in each direction, the MD stretching ratio is preferably 2 to 4 times, more preferably 2.5 to 3.5 times, and further preferably TD stretching ratio is 3 to 5 times, more preferably It is 3.5 to 4.5 times.

At the same time, after biaxial stretching, it is preferred to perform heat fixation so that the TD relaxation rate is 3.0 to 7.0%. The heat setting temperature is preferably from 140 to 185 ° C, more preferably from 155 to 180 ° C.

Further, the unstretched film can be subjected to a preliminary longitudinal extension of about 1.2 times or less before being introduced into the simultaneous biaxial stretching machine.

Further, the polyester film of the present invention can be produced by a sequential biaxial stretching method.

In the sequential biaxial stretching method, the unstretched film obtained by the above method is heated by a roll or infrared rays or the like, and is extended in the longitudinal direction (MD) by using a difference in rotation speed of two or more rolls at 50 to 150 ° C. Stretch film. In the longitudinal extension, the MD stretching ratio is preferably 2 to 4 times. More preferably 2.5 to 3.5 times.

The obtained longitudinally stretched film is then continuously stretched in the width direction (TD) to form a biaxial alignment film. The width direction (TD) extension starts at 50 to 150 ° C, and the TD stretching ratio is preferably 3 to 5 times, more preferably 3.5 to 4.5 times.

Even in the case of successive two-axis extension, it is the same as the above-mentioned simultaneous two-axis extension For the reason, the area magnification (MD stretching ratio × TD stretching ratio) is preferably 6 to 20 times, more preferably 8.75 to 15.75 times, and the stretching ratio ratio (MD stretching ratio / TG stretching ratio) is preferably 0.4 to 1, more preferably Good is 0.55 to 1, and particularly preferably 0.75 to 0.85.

After the secondary biaxial stretching, it is preferred to perform heat fixation so that the TD relaxation rate is 3.0 to 7.0%. The heat setting temperature is preferably from 140 to 185 ° C, more preferably from 155 to 180 ° C.

At the same time, the heat-fixing treatment after the biaxial stretching or the sequential two-axis stretching is an important step for imparting dimensional stability to the film. In this method, a known method such as a method of blowing hot air, a method of irradiating infrared rays, or a method of irradiating microwaves can be used. Among them, since it can be heated uniformly and with high precision, it is most suitable for blowing hot air.

In order to achieve better passability in the cold roll forming of the obtained laminated film during the production of the polyester film of the present invention, it is preferred to form a film by adding a small amount of an inorganic lubricant such as cerium oxide, aluminum oxide or kaolin to the raw material polyester. In order to impart lubricity to the surface of the polyester film. The content of the inorganic lubricant in the polyester film is preferably from 0.001 to 0.5% by mass, more preferably from 0.05 to 0.3% by mass.

Further, in order to enhance the appearance or printability, the polyester film may contain, for example, a polyoxymoxide or the like.

The polyester film of the present invention preferably contains from 2000 to 6000 ppm of an incompatible low molecular weight polyethylene in the polyester constituting the film. When the content of the low molecular weight is less than 2,000 ppm, the effect of improving the lubricity is insufficient. On the other hand, when the content exceeds 6000 ppm, the quality of the film surface is excessively lubricated, and the polyester film becomes brittle due to the excessive amount of the non-compatible resin.

The low molecular weight polyethylene in the present invention preferably has a number average molecular weight of from 1,000 to 8,000, more preferably from 2,000 to 6,000. If the low molecular weight polyethylene having a molecular weight in the above range is contained in the non-compatible polyester, the surface of the film can be roughened to improve lubricity, and The resulting laminate film can be maintained on a rough film surface. When the number average molecular weight of the low molecular weight polyethylene is less than 1,000, the molecular weight is too low, and the surface of the film may be peeled off during film processing or film formation, and the jig may be contaminated in the cold rolling forming step, and the film may be damaged. The situation itself. On the other hand, when the number average molecular weight of the low molecular weight polyethylene exceeds 8,000, the effect of roughening the surface of the obtained laminated film is insufficient, and the lubricity at the time of cold rolling forming is deteriorated.

The method of adding the low molecular weight polyethylene to polybutylene terephthalate (PBT) and polyethylene terephthalate (PBT) is not particularly limited, but it is preferably prepared in an amount of 0.5 to 5% by mass in advance. A masterbatch of low molecular weight polyethylene, and a masterbatch is added to the polybutylene terephthalate (PBT) and polyethylene terephthalate (PBT) or a mixture thereof.

The laminated film of the present invention is a layer in which a metal foil and a sealing film are sequentially laminated on the polyester film of the present invention.

Examples of the metal foil include aluminum platinum, copper platinum, tin platinum, gold platinum, silver platinum, zinc platinum, brass platinum, nickel platinum, stainless steel platinum, iron platinum, titanium platinum, and the like.

The metal foil may be a chemical treatment such as chromic acid treatment, phosphoric acid treatment, electrolytic chromic acid treatment, chromate treatment, or nickel, tin, zinc, aluminum, gunmetal, brass, or the like. By.

The thickness of the metal foil is preferably from 9 to 60 μm, more preferably from 20 to 50 μm. When the thickness of the metal foil is less than 9 μm, the pinhole ratio of the metal foil is high, and when the laminated film having the metal foil is used as a lithium ion secondary battery, the defective ratio is improved. On the other hand, when the thickness exceeds 60 μm, the stress at the time of cold rolling forming becomes high, and the metal foil in the laminated film is likely to be broken or the polyester film is broken.

A method of laminating a polyester film on a metal foil, which is a translucent adhesive The method of layering the layers.

The resin to be used as the adhesive is not particularly limited, and a resin such as a polyester resin, an epoxy resin, a polyurethane resin, or a polyester-epoxy copolymer resin is used as a main component, and a melamine resin or an isocyanate resin is used. One or two or more kinds of oxazoline resins and phenol resins are used as an adhesive for the curing agent. The adhesive layer provided with such an adhesive is suitable for cold rolling forming.

The subsequent layer can be provided by coextrusion, lamination, or coating.

The thickness of the subsequent layer is preferably from 0.5 to 5.0 μm. When the thickness of the layer is less than 0.5 μm, the adhesion is insufficient. When the thickness exceeds 5.0 μm, the adhesion of the adhesive, the workability, and the cohesive force after the processing are lowered. In either case, the laminated film is formed in the middle of the molding. Produces a film peeling flaw.

The laminated film of the present invention is a laminate in which a sealing film is laminated on a metal foil which has been laminated on a polyester film. The laminated film can be hermetically sealed into a bag body by having a sealing film.

The sealing film is preferably made of polyethylene, polypropylene, maleic acid modified polypropylene, maleic acid modified polyethylene, ethylene-acrylate copolymer, ionic polymer resin, in view of excellent sealing property and chemical resistance. An unstretched film composed of polyvinyl chloride or the like.

The method of laminating the sealing film on the metal foil is the same as the method of laminating the polyester film on the metal foil as described above.

Example

The invention will be described in detail below by way of examples, but the invention is not limited to the examples described below.

In the production of the polyester film, the following resins were used.

PBT-1: PBT with solid phase polymerization, ultimate viscosity 1.08 dl/g, Tm 223 ° C, containing 40 ppm of Ti catalyst.

PET-1: PET subjected to solid phase polymerization, ultimate viscosity 0.75 dl/g, Tm 255 ° C, containing 40 ppm of Ge catalyst.

PET-2: 6 mol% of isophthalic acid copolymerized PET subjected to solid phase polymerization, an ultimate viscosity of 0.75 dl/g, Tm 233 ° C, and a 40 ppm Ge catalyst.

PET-3: 15 mol% of isophthalic acid copolymerized PET subjected to solid phase polymerization, an ultimate viscosity of 0.75 dl/g, a Tm of 215 ° C, and a 40 ppm Ge catalyst.

The properties of the raw material resin, the polyester film, and the laminated film were measured or evaluated by the following methods.

A. Resin ultimate viscosity

0.25 g of the resin was dissolved in 50 ml of phenol/tetrachloroethane = 5/5 (mass ratio), and was measured at 25 ° C using a Ubbelohde viscometer.

B. Resin, polyester film melting point (Tm)

The melting point at a temperature rise of 20 ° C / min was measured using DSC manufactured by Perkin Elmer Co., Ltd.

The measurement sample of the polyester film was obtained by melting the film and quenching at a rate of 100 ° C/min or more to become amorphous. Two melting points were observed in each of the examples and comparative examples, but the lower one (Tm1) was derived from polybutylene terephthalate (PBT), and the higher (Tm2) was derived from polyterephthalic acid. Ethylene glycol (PET).

C. Thermal shrinkage of polyester film

As a test piece for measuring the heat shrinkage rate in the longitudinal direction (MD) of the film, five test pieces in which two polyester lines were cut into TD10 mm × MD 150 mm and two lines were cut at intervals of 100 mm were prepared.

Similarly, as a test piece for measuring the heat shrinkage ratio in the width direction (TD) of the film, Five test pieces were prepared in which the polyester film was cut into MD 10 mm × TD 150 mm and two lines were drawn at intervals of 100 mm.

The obtained test piece was heat-treated in a 160 ° C oven for 15 minutes under no load, and the test piece was taken out to return to room temperature, and the distance between the lines was measured. The heat shrinkage ratio was determined by the following formula, and the average value of the five sheets was taken as the MD heat shrinkage ratio and the TD heat shrinkage ratio.

Heat shrinkage rate (%) = (A-B) / A × 100

A: distance between marking lines before heat treatment (mm), B: distance between marking lines after heat treatment (mm)

D. Transesterification index (Ex)

The ¹³ C NMR measurement was carried out on a GEMINI 2000/300 nuclear magnetic resonance apparatus (magnetic field strength: 7.5 T) manufactured by Varian. The measurement sample was obtained by dissolving 60 to 100 mg of the membrane in 0.7 ml of a CF ₃ COOD solvent, and the transesterification index (Ex) was obtained from the integral value derived from the transesterification peak (Fig. 1) by the following formula.

Ex(%)=(Sab+Sba)/(Saa+Sbb+Sab+Sba)×100

E. Resistance of polyester film to electrolyte, acid resistance to hydrofluoric acid

One drop of electrolyte solution was dropped on the surface of the polyester film (lithium tetrafluoroborate was dissolved in a concentration of 1 mol/L in an ethylene carbonate/diethyl carbonate mixed solvent (mass ratio 1/1)), and hydrofluoric acid ( 47%), and observe the surface state of the film separately. The resistance to the electrolyte and the acid resistance to hydrofluoric acid were evaluated as ○ in the case where the film was not opened within 10 minutes after the dropping, and evaluated as ╳ in the case of the opening.

F. Formability of laminated film

Using a 1ton table automatic extruder (SBN-1000 manufactured by Yamaoka Seisakusho Co., Ltd.), a laminate film of 115 mm × 115 mm × depth of 6 mm was used, and the laminated film was formed by cold rolling from the side of the sealing film (unextended polypropylene film). The formability was evaluated.

In the laminated film after molding, no cracks or delamination occurred, and the appearance of the molded portion and the periphery thereof without wrinkles and film whitening was evaluated as ◎, and no crack or interlayer peeling was evaluated as ○, and the aluminum foil was not penetrated but cracked. On the other hand, those who did not cause interlayer peeling were evaluated as Δ, and those who penetrated the aluminum foil and caused cracks or who produced interlayer peeling were evaluated as ╳.

Example 1

In 60 parts by mass of polybutylene terephthalate (PBT-1) and 40 parts by mass of polyethylene terephthalate (PET-1), an average particle diameter of 2.5 μm is added in such a manner that the content is 0.08% by mass. The agglomerated cerium oxide was melted at a temperature of 275 ° C for a residence time of 5 minutes, extruded from the outlet of the T die, and then rapidly solidified to obtain an unstretched film.

The unstretched film is then extended using a tenter type sequential stretcher. First, the unstretched film was heated by a roll in a longitudinal stretcher, extending 3.39 times in MD, then starting horizontally at 80 ° C, and extending 3.84 times in TD. In this extension, the area magnification (MD stretching ratio × TD stretching ratio) was 13, and the stretching ratio ratio (MD stretching ratio/TD stretching ratio) was 0.88.

The heat setting temperature was 167 ° C, the TD relaxation rate was 5%, and the heat treatment was performed for 4 seconds, and then cooled to room temperature and rolled up to obtain a polyester film for cold roll forming having a thickness of 25 μm.

On the obtained polyester film for cold-rolling, an aluminum foil (AA8079 made of Light Aluminum Foil Co., Ltd., thickness 40 μm) and an unstretched polypropylene film as a sealing film were laminated by a dry lamination method (Mitui Chemical Tohcello Co., Ltd.) The GHC was prepared to have a thickness of 40 μm, and subjected to a 72-hour ageing treatment in an environment of 60 ° C to prepare a laminated film. Further, the adhesive was TM-K55/CAT-10L (mixing ratio of 100/10) manufactured by Toyo Morton Co., Ltd., and the coating amount was 4.0 g/m ² .

Examples 2 to 23 and Comparative Examples 1 to 5

In addition to changing the ratio of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), as shown in Table 1, the type of polyethylene terephthalate (PET) (m-benzene) A polyester film for cold rolling molding and a laminated film were obtained in the same manner as in Example 1 except that the copolymerization ratio of dicarboxylic acid, the MD stretching ratio, the TD stretching ratio, and the heat setting temperature were carried out.

The properties of the polyester film and the laminated film obtained in Examples 1 to 23 and Comparative Examples 1 to 5 are shown in Table 1.

Example 24

An unstretched film was obtained in the same manner as in Example 1.

Then, the end of the unstretched film is clamped to the clip of the tenter type simultaneous biaxial stretching machine, and after passing through the preheating zone of 60 ° C, the MD is 3.0 times and T is 3.3 times at the temperature of 80 ° C. extend. In this extension, the area magnification (MD stretching ratio × TD stretching ratio) was 9.9, and the stretching ratio ratio (MD stretching ratio/TD stretching ratio) was 0.91.

Then, the relaxation rate of TD was 5%, and the heat treatment was carried out for 4 seconds at a heat setting temperature of 165 ° C, and then cooled to room temperature and rolled up to obtain a polyester film for cold roll forming having a thickness of 25 μm. In the obtained polyester film for cold-rolling, a metal foil and a sealing film were dry-laid in the same manner as in Example 1 to form a laminated film.

Examples 25 to 29 and Comparative Examples 6 to 7

In addition to the changes shown in Table 2, the ratio of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), the type of polyethylene terephthalate (PET), heat fixation The polyester film and the laminated film for cold-rolling were obtained in the same manner as in Example 24 except for the temperature.

Example 30

A polyester film for cold-rolling molding and a laminated film were obtained in the same manner as in Example 24 except that the unstretched film obtained by melting at 285 ° C for 15 minutes was used.

Comparative Example 8

A polyester film for cold-rolling molding and a laminated film were obtained in the same manner as in Example 1 except that a polyester film (Bonyl RX, thickness: 25 μm, manufactured by Higashi Co., Ltd.) was used in place of the polyester film.

Polyester film and laminate obtained in Examples 24 to 30 and Comparative Examples 6 to 8 The properties of the film are shown in Table 2.

In the examples 1 to 30, the obtained polyester film was excellent in acid resistance and electrolyte resistance, and was excellent in the formed film formability. Among them, in Examples 2, 3, 5, and 7, the ratio of the stretching ratio of the polyester film was particularly excellent, so that the alignment balance was particularly excellent, and in Examples 4 and 6, the polyethylene terephthalate contained the content. By using phthalic acid as an acid component, the crystallization is suppressed, and the moldability is improved, and a laminated film having excellent moldability and a good appearance after molding is obtained.

In Examples 10 and 13, the surface magnification of the polyester film was out of the preferred range. Further, in Examples 14 and 17, the stretch ratio of the polyester film was outside the range of the preferred ratio, so that the alignment balance was poor and concentrated. In addition, in Examples 18 to 19, in order to suppress the crystallization in the film, the moldability was improved, and when the heat setting temperature was set to be slightly lower, the residual stress in the film became high, and in addition, in Examples 20 to 21, in order to make the film When the residual stress is lowered and the heat setting temperature is set to be slightly higher, the film is crystallized, and the laminated film after the formation of the two layers does not penetrate the crack of the aluminum foil, but does not cause interlayer peeling. There is no problem.

In Comparative Examples 1 and 6, the content of polybutylene terephthalate (PBT) in the polyester film was large, and the properties of polybutylene terephthalate (PBT) having high crystallinity were apparently exhibited, and the obtained laminated film was not Excellent formability. In Comparative Example 2, the heat setting temperature was high and the crystallization of the polyester film was progressed, so that the stress of the film during molding was increased, and the content of polybutylene terephthalate (PBT) was large, and the crystallinity was high. The properties of the polybutylene terephthalate (PBT), the resulting laminate film is broken by the aluminum foil, and is not excellent in formability.

In Comparative Examples 3 to 5 and 7, the content of polybutylene terephthalate (PBT) in the polyester film was small, and the film stress during molding was high, and in Comparative Examples 4 to 5, the heat setting temperature was high and The crystallization of the polyester film proceeds, and the laminated film obtained by the two produces an aluminum foil. Crack, not excellent in formability.

In Comparative Example 8, although a laminated film having excellent moldability was obtained, the polyamide film constituting the same did not have acid resistance or electrolyte resistance.

Claims (7)

A polyester film for cold rolling forming, comprising polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), wherein the mass ratio of PBT to PET (PBT/PET) is 30/70 to 80/20. The polyester film for cold-rolling forming according to claim 1, wherein the heat-shrinkage ratio in the longitudinal direction (MD) and the heat-shrinkage ratio in the width direction (TD) are 5 after heat treatment at 160 ° C for 15 minutes. Up to 20%. The polyester film for cold-rolling forming according to claim 1, wherein the polyethylene terephthalate (PET) contains 0 to 15 mol% of phthalic acid as an acid component. The polyester film for cold-rolling forming according to claim 1, wherein the transesterification index of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) is 1 to 10%. A method for producing a polyester film for cold-rolling forming, which is a polyester film for cold-rolling forming according to any one of claims 1 to 4, wherein the polyester film is in a long direction (MD) The width direction (TD) is extended so that the area magnification (MD stretching ratio × TD stretching ratio) is 6 to 20 times, and the stretching ratio (MD stretching ratio / TD stretching ratio) is 0.4 to 1. The method for producing a polyester film for cold-rolling forming according to claim 5, wherein the MD stretching ratio is 2 to 4 times and the TD stretching ratio is 3 to 5 times. A laminated film in which a metal foil and a sealing film are sequentially laminated on the polyester film for cold-rolling forming according to any one of claims 1 to 4.